The present invention relates to a thrust ball bearing positioned between two members carrying out eccentric rotating movements relative to one another, such as a swivel scroll member and a stationary scroll member in a vehicle air conditioning scroll compressor.
In the FIGS. 1-3, there is shown a known scroll compressor 10 including a housing 11 in which are positioned a swivel scroll member 12 and a stationary scroll member 13. The stationary scroll member 13 is fixed to the housing 11 and the swivel scroll member is free to rotate inside the housing 11. The swivel scroll member 12 is provided with spiral partitions 14 extending toward the stationary scroll member 13 and the stationary scroll member 13 is provided with spiral partitions 15 extending toward the swivel scroll member 12. The partitions 14 and cooperate to form a compression chamber 16 having a capacity that is varied in accordance with the eccentric rotations of the swivel scroll member 12 with respect to the stationary scroll member 13 thereby compressing a fluid in the compression chamber 16.
A central axis 17 of the swivel scroll member 12 is aligned with a longitudinal axis of an eccentric end 18 of a drive shaft 19 rotated by a drive motor 20. The drive shaft 19 has a main longitudinal axis 21 that is offset from the central axis 17 by a distance "A" such that as the drive motor 20 rotates the drive shaft 19, the swivel scroll member 12 eccentrically rotates at a swivel radius equivalent to the eccentricity amount "A". During operation, a thrust load is imposed in an axial direction upon the rotating swivel scroll member 12 by compression cycles of the fluid in the compression chamber 16. In order to support the thrust load, a thrust ball bearing 22 is disposed between the swivel scroll member 12 and the housing 11.
The bearing 22 includes a pair of bearing rings 23 having the same shape and same dimension and a plurality of balls 24 disposed between the bearing rings. As shown in the FIG. 2, the bearing rings 23 each have a generally planar annular body 25 with a plurality of annular bearing races 26 open to one planar surface 27. The races 26 are formed as depressions or grooves in the surface 27. As shown in the FIG. 1, one of the rings 23 is mounted in an annular recess 28 formed in a surface of the housing 11 facing the swivel scroll member 12 and the other ring 23 is mounted in a similar recess 29 formed in a surface of the swivel scroll member 12 facing the housing 11.
The balls 24 are retained in the facing races 26 as shown in the FIGS. 1 and 3. The balls 24 in the respective races 26 roll on a pitch circle 30 corresponding to the eccentric rotations of the swivel scroll member 12. The pitch circle 30 is the lowest portion of the race wall which is curved at a predetermined radius. A diameter "B" of the pitch circle 30 is equal to the eccentricity distance "A".
In the conventional thrust ball bearing 22, the bearing rings 23 are of the same shape and same dimensions, and the groove curvatures of the races 26 are the same. The curvatures of the races 26 have a larger radius than a radius of the balls 24 to decrease the contact pressures with the balls to increase the service life thereof. The use of identical rings 23 decreases manufacturing, assembly and replacement parts costs.
However, manufacturing tolerances may cause the races 26 to be misaligned upon assembly of the bearing 22. One known solution to this problem is to make the radius of curvature of one of the races 26 larger than the radius of curvature of the facing race to accommodate axial misalignment. If the smaller and larger diameter races are alternated, a pair of identical rings can be utilized in the thrust bearing assembly.
It is also known to make the rings 23 of different thickness.